1. Field of the Invention
Embodiments of the invention primarily relate to ionizing devices that are used for static charge neutralization and control. More specifically, embodiments of the invention are targeted at the need for reliable and low particle emission ionizers within the semiconductor, electronics, and/or flat panel industries.
With AC ionizers, each emitter receives a high positive voltage during one time period and a high negative voltage during another time period. Hence, each emitter generates corona discharge with output of both positive and negative ions.
A stream (cloud) of positive and negative ions is directed toward a charged target(s) for the purpose of neutralizing the charges and preventing static charge associated technological problems.
2. Description of Related Art
The background description provided herein is for the purpose of generally presenting the context of the present disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this present disclosure.
Ion emitters of charge neutralizers generate and supply both positive ions and negative ions into the surrounding air or gas media. To generate gas ions, the amplitude of the applied voltage must be high enough to produce a corona discharge between at least two electrodes arranged as an ionization cell. In the ionization cell, at least one electrode is an ion emitter and another one may be a reference electrode. Also it is possible that the ionization cell includes at least two ionizing electrodes.
Along with useful positive gas ions and negative gas ions, emitters of charge neutralizers may create and emit corona byproducts including unwanted particles. In a semiconductor process and similar clean processes, particle emission/contamination correlate with defects, product reliability problems, and lost of profits.
Several known in the art factors influence the quantity of unwanted particles emission. Some of primer factors include, for example, the material composition, geometry, and design of the ion emitter. The second one includes the arrangement of the emitter connection to a high voltage power supply. Another critical factor is associated with a profile of electrical power (magnitude and time dependence of high voltage and current) that is applied to the ion emitters.
The power waveforms can be used to control the voltage profile that is applied to the emitters by the high voltage power supplies. Voltage/current waveforms can be used to control both ion generation and particle emission by emitter(s).
Corona discharge can be energized by DC (direct current) voltage, AC (alternating current) voltage, or a combination of both voltages. For many applications of this invention, a preferable power waveform is a high frequency high voltage (HF-HV) output from a high frequency (HF) power supply, as will be discussed below. This high voltage output may be continual rather than continuous. That is, the voltage output may be variable by amplitude in time or turned off periodically.
The material composition of emitters is known to affect particle emission levels of ionizers. Common emitter materials include stainless steel, tungsten, titanium, silicon oxide, single crystal silicon, silicon carbide, and other nickel or gold plated metals. This list is not complete. From the experience of the inventors, metallic type emitters are prone to generate more particles as a result of corona associated erosion and spattering. Moreover, metallic or, in general, highly conductive particles are often considered as “killer particles” in the semiconductor industry (i.e., the particles are able to short-circuit tightly positioned conductive traces of wafers/chips). So, in the frame of this patent application the inventors basically consider non-metallic ion emitters, as will be discussed below.
In one of these materials, a super clean (more than 99.99% plus purity) single crystal silicon is suggested by Scott Gehlke in U.S. Pat. No. 5,447,763 from the viewpoint of low particle emission. This single crystal silicon has been adopted by the semiconductor industry as a de-facto clean emitter standard. A super clean silicon carbide (at least 99.99% pure) suggested by Curtis et al. in U.S. patent application publication No. 2006/0071599 is another non-metallic material. However, silicon carbide emitters are expensive and prone for emission of undesirable particles.
Known ionizers with single crystal silicon emitters are powered by two high voltage DC supplies. A system, like the room ionization system “NiLstat” 5000 (Ion Systems, Inc.) for cleanroom ceiling installation, typically produces less than 60 particles per cubic foot of air that are greater than 10 nanometer (diameter). Other emitter materials typically produce more than 200 particles per cubic foot of air that are greater than 10 nanometer (diameter). Some materials produce thousands of particles per cubic foot of air that are greater than 10 nanometer (diameter).
Although some of (1) components of emitter materials, (2) elements of connector construction for a non-metallic emitter, and (3) application of special power waveforms may be known to be independently important, the prior art has not considered the benefits of strategically combining these factors to reach high ionization reliability and cleanliness.
Recent experiments by the inventors have resulted in the inventors discovering and finding novel combinations that lead to stable ion production and unpredictably low levels of particle generation by the emitter. Clean and/or low particle emission ionizers have utility in several high technology industries. In particular, the semiconductor industry has a well-defined need for super clean ionizers. The ionizers are needed to minimize static charges and electrical fields, which can destroy semiconductor devices. As low as possible particle emission is also required because foreign particles may compromise the reliability of semiconductor devices. Leading edge semiconductor technology is building 24-16 nanometer features on wafers. For the nanometer features, control of particles greater than 10 nanometers is absolutely needed.
It is to be understood that both the foregoing general description in the background section are exemplary and explanatory only and are not restrictive of the invention, as claimed.